Calotropis procera (Aak/Madar) as an Emerging Reservoir of Begomoviruses: A Critical Appraisal of the Evidence, Its Methodological Limits and its Epidemiological Significance

Abstract

Begomoviruses (genus Begomovirus, family Geminiviridae) transmitted by the whitefly Bemisia tabaci impose severe and recurrent losses on vegetable, fibre and ornamental production across the tropics and subtropics. Non-cultivated plants are increasingly ecognized as reservoirs that sustain viral populations between cropping seasons and provide arenas for recombination, yet the reservoir literature has concentrated on a narrow set of herbaceous annual weeds. Calotropis procera (Aiton) Dryand. Occupies an unusual position within this problem. It is a perennial, evergreen, latex-bearing shrub of arid and semi-arid landscapes, a widely used ethnomedicinal plant across South Asia, West Asia and North Africa, and an aggressive colonist of field margins, roadsides and fallow land. This review critically evaluates the evidence that C. procera functions as a begomovirus reservoir, examines the methodological basis of the available records, and situates the species within current epidemiological frameworks. Literature was retrieved from open scholarly indexes and appraised for design adequacy, inferential strength and evidence-claim alignment. The available evidence establishes natural begomovirus infection of C. procera by at least two distinct virus-satellite configurations reported from the Indian subcontinent, comprising a monopartite virus with an associated betasatellite and a bipartite virus recovered without satellites. Support for reservoir function, as distinct from host susceptibility, is considerably weaker. No published study has demonstrated whitefly-mediated acquisition from, or transmission to, this species, no infectivity assay using cloned components has been reported for the recovered genomes, and no survey has quantified infection prevalence, seasonal persistence or spatial association with adjacent crop epidemics. The perennial, drought-tolerant habit of the species makes off-season persistence mechanistically plausible, but plausibility has repeatedly been reported as though it were demonstration. Confidence in the current picture is further limited by reliance on symptom-guided sampling, small numbers of sequenced isolates, and the absence of records from the extensive African and Australasian range of the plant. Resolving whether this shrub is an epidemiologically consequential reservoir or an incidental dead-end host requires transmission experiments, prevalence surveys anchored to crop disease gradients, and sequence sampling designed for population-level inference.